The present invention relates to a method of aerating a liquid. The invention is particularly useful for aerating wastewater in the treatment of the wastewater for re-use, and is therefore described below with respect to such an application.
The activated sludge process of wastewater treatment is an aerobic, suspended-growth, process that maintains a relatively high population of microorganisms (biomass) by recycling settled biomass back to the treatment process. The biomass converts soluble and colloidal biodegradable organic matter and some inorganic compounds into cell mass and metabolic end products. The biomass is separated from the wastewater through settling in a settling tank, or clarifier, for recycling or wasting to sludge handling processes.
Preliminary treatment to remove settleable solids and floatable materials is usually provided by a septic tank or other primary treatment device. Most onsite designs are capable of providing significant ammonia oxidation and effective removal of organic matter.
A basic system consists typically of the following interrelated components:
1. an aeration tank or basin;
2. an oxygen source and equipment to disperse atmospheric or pressurized air or oxygen into the aeration tank at a rate sufficient to always maintain positive dissolved oxygen;
3. a means to appropriately mix the aeration basin and ensure suspension of the biomass (usually accomplished by the aeration system); and
4. a settling tank or clarifier to separate the biomass from the treated effluent and collect settled biomass for recycling to the aeration basin.
However, in the existing wastewater treating systems the amount of oxygen capable of being dissolved in the water is limited, thus limiting the biomass growth and the capacity and rate of wastewater treatment.
A number of techniques have been proposed in the patent literature for increasing the amount of oxygen dissolved in the wastewater being treated in order to enhance the biomass growth. For example, U.S. Pat. No. 6,153,099 describes an apparatus including a series of open vessels each equipped with a nozzle for discharging a spray of the wastewater into the respective vessel. U.S. Pat. Nos. 4,274,959 and 4,369,111 describe systems including pressurized containers for aerating the wastewater.